Method of preparing propellant charges from fibrous nitrocellulose

ABSTRACT

A process for preparing propellant charges from fibrous nitrocellulose is provided. The fibrous nitrocellulose is plasticized and then molded into a consolidated charge in which the fibers retain their individual identity. The propellant charges can be used as caseless cartridges for caseless ammunition.

@3108 aem Dehm et a1.

1 51 July 11, 1972 [54] METHOD OF PREPARING PROPELLANT CHARGES FROM FIBROUS NITROCELLULOSE [72] Inventors: Henry C. Dehm, Salt Lake City, Utah;

[52] U.S. Cl. ..264/3 C, 149/2, 149/96, 149/98, 149/100, 102/38 [51] Int. Cl. ..C06b 21/02 [58] Field of Search ..264/3; 149/9, 11, 12, 96, 97, 149/98, 100; 102/38 [56] References Cited UNITED STATES PATENTS 1,862,914 6/1932 Wagner ..149/12 2,235,298 3/1941 Olsen ..149/12 2,344,516 3/1944 McBride ..149/12 2,946,673 7/1960 Grassie ..264/3 UX 2,991,168 7/1961 Nadel ..149/98 X 3,290,190 l2/1966 Godfrey et al. .....264/3 X 3,378,611 4/1968 Kincaid et al.... ..264/3 3,398,684 8/ l 968 Kvavle l02/49.3 3,422,169 l/l969 Brooks et al.. .....264/3 3,447,983 6/1969 Camp et al.... 149/98 3,463,086 8/1969 Silva et a1. ..102/38 2,988,436 6/1961 ONeill .149/97 X 3,092,525 6/1963 Cook ..149/97 X Primary Examiner-Carl D. Quarforth Assistant Examiner-Stephen J. Lechert, Jr. Attorney-Michael B. Keehan [57] ABSTRACT A process for preparing propellant charges from fibrous nitrocellulose is provided. The fibrous nitrocellulose is plasticized and then molded into a consolidated charge in which the fibers retain their individual identity. The propellant charges can be used as caseless cartridges for caseless ammunition.

6 Claims, No Drawings METHOD OF PREPARING PROPELLANT CHARGES FROM FIBROUS NITROCELLULOSE This invention relates to a process for manufacturing propellant charges from fibrous nitrocellulose. More particularly, this invention relates to a process for making caseless cartridges from fibrous nitrocellulose.

Caseless cartridges are now prepared by molding of smokeless powder granules employing a volatile solvent for nitrocellulose with or without nitrocellulose dissolved in the solvent. The solvent softens the surface of the granules which are bonded together during molding. In this process the smokeless powder granules are admixed with the solvent, the admixture charged to a mold and subjected to molding pressure, and a molded charge recovered. The molded charge is dried to remove the volatile solvent contained in the charge and then machined to size. This process is expensive, due to the number of processing steps.

We have now discovered a process for manufacture of propellant charges from fibrous nitrocellulose having useful ballistic properties. This process eliminates the costs for separate production of smokeless powder and provides a precision molded propellant charge that is dimensionally stable. The drying step of prior art processes and the necessity for machining the molded charge are eliminated.

in accordance with this invention, a process for preparing propellant charges is provided which comprises admixing fibrous nitrocellulose with a solution of nitrocellulose plasticizer in a volatile non-solvent for nitrocellulose to provide plasticized fibrous nitrocellulose fibers, removing the volatile solvent from the plasticized fibrous nitrocellulose fibers, molding the resulting solvent free plasticized fibrous nitrocellulose fibers and recovering a consolidated propellant charge in which the individual fibers of the fibrous nitrocellulose retain their identity.

The fibrous nitrocellulose that can be employed in this invention has a nitrogen content of from about 10.5 percent to about 13.5 percent nitrogen. A preferred fibrous nitrocellulose is dynamite grade nitrocellulose which is a fibrous nitrocellulose having a nitrogen content of about 12.2 percent. The fibrous nitrocellulose can have a viscosity range of from about one-half second to about 200,000 seconds as measured according to ASTM D 301.

The nitrocellulose plasticizers employed in this invention are dissolved in a volatile solvent which is a non-solvent for the nitrocellulose, prior to mixing with the fibrous nitrocellulose. Representative plasticizers which are energetic plasticizers for nitrocellulose include nitroglycerin, butane triol trinitrate, diethylene glycol dinitrate, methylene dinitramine, n-methylethylnitramine, n-methyl beta-nitroxyethylnitramine, and the like. These energetic plasticizers can be mixed with one or more miscible relatively low energy plasticizers such as triacetin, dibutyl phthalate, tricresylphosphate, tributoxyethylphosphate, dimethyl sebacate, dibutyl succinate, adiponitrile, and the like.

When it is desired to prepare a propellant charge of single base composition, any of the above low energy plasticizers or mixtures thereof can be employed with the fibrous nitrocellulose. The energetic plasticizer is omitted.

Suitable volatile solvents for the plasticizers of this invention which are nonsolvents for nitrocellulose include propanol, isopropanol, butanol, isobutanol; the lower aliphatic hydrocarbons such as hexane, heptane, octane, isooctane, and the like; aromatic hydrocarbons such as benzene, toluene, and xylene; and halogenated hydrocarbons such as methylene chloride and trichloroethylene. Mixtures of two or more plasticizer solvents can be employed if desired.

In preparing the solution of plasticizer in volatile solvent, the weight ratio of solvent to plasticizer should generally be kept at the minimum level. This minimizes the amount of solvent which must be removed from the plasticized fibrous nitrocellulose fibers. For most solvent-plasticizer solutions this weight ratio will vary from about 5:1 to about :1.

The weight ratio of fibrous nitrocellulose to plasticizer employed is dependent upon the desired composition of the final molded propellant charge. Substantially all of the plasticizer contained in the plasticizer solution is absorbed by the fibrous nitrocellulose. In general, the weight ratio of plasticizer to fibrous nitrocellulose will vary from about 1:9 to about 3:7. When the desired amount of plasticizer to be incorporated into the fibrous nitrocellulose fibers is at a low weight ratio, additional volatile solvent can be employed in order to facilitate mixing and insure uniform plasticization of the fibrous nitrocellulose fibers.

Mixing time required for the fibrous nitrocellulose to become plasticized with the desired amount of plasticizer will vary with mixing temperature and plasticizer composition. Mixing times for fibrous nitrocellulose which is to be highly plasticized are longer than for fibrous nitrocellulose in which a small amount of plasticizer is employed. In general, mixing times at 20 C. will vary from about 5 minutes to about 1 hour.

Following plasticization of the fibrous nitrocellulose with plasticizer, the volatile solvent employed is removed by any convenient method. For large scale operations the plasticized fibrous nitrocellulose can be centrifuged to remove the bulk of the solvent from the fibers, and the remaining solvent removed by stripping at reduced pressures.

The plasticized fibrous nitrocellulose fibers are molded to provide a strong propellant charge. In general, suitable molding conditions include molding temperatures of from about 20 C. to about C., molding pressures of from about 500 psi to about 25,000 psi, and mold dwell time, which is defined as the time the plasticized fibrous nitrocellulose is in the mold under compression conditions, of from about 1 second to about 1 minute. Molding conditions, however, for any particular plasticized fibrous nitrocellulose composition are dependent on the size of the propellant charge to be molded and must be chosen so that the plasticized fibrous nitrocellulose fibers retain their identity as plasticized fibers in the molded propellant charge. This is necessary to achieve good ballistic performance. Molded propellant charges in which the nitrocellulose fibers do not retain their identity are transparent rather than opaque, and are homogeneous.

Preferred molding conditions for molding plasticized dynamite grade fibrous nitrocellulose and employing a plasticizer comprised of nitroglycerin are mold temperatures of about 35 C. to about 50 C., molding pressures of about 12,000 to about 16,000 psi, and a mold residence time of about 1 to about 10 seconds.

Propellant charges prepared in accordance with the process of this invention have higher burning rates and develop higher chamber pressures than propellant charges prepared from molded smokeless powder. It may be necessary in some applications to increase the chamber volume in which the charge is burned to achieve the overall ballistic results desired.

The following examples will further illustrate the process of this invention. All parts and percentages are by weight unless otherwise specified.

EXAMPLE 1 Exactly 15 parts of nitroglycerin, 10 parts of triacetin, and 5 parts of tricresylphosphate are dissolved in 250 parts of isopropanol. The resulting solution is added to 70 parts of dynamite grade fibrous nitrocellulose having 12.2 percent nitrogen content and a viscosity of about 200,000 seconds as measured according to ASTM D 301. The admixture is agitated for about 5 minutes until the fibrous nitrocellulose has absorbed substantially all of the plasticizer in the plasticizer solution. The isopropanol solvent is then stripped from the admixture at ambient temperature (70 F.) and at a reduced pressure of about 5 mm Hg. Free-flowing plasticized nitrocellulose fibers are recovered having the following composition:

Fibrous nitrocellulose 70% Nitroglycerin 15% Triacetin 10% EXAMPLE 2 A 5.56 mm propellant mold is charged with 23.13 grams of plasticized fibrous nitrocellulose fibers prepared in Example 1. The plasticized fibrous nitrocellulose fibers are compressed at 7,000 psi for 40 seconds at a mold temperature of 75 F. An opaque propellant charge is recovered. The charge is strong, dimensionally stable, and chambers easily in a 5.56 mm test weapon without need of machining. The charge is assembled with a shot shell primer, with 1.0 gram of smokeless powder booster, and with a 55 grain jacketed bullet. Four additional rounds are prepared as described. The assembled rounds of caseless ammunition are fired in a 5.56 mm test weapon. Results of test firings are as follows:

Muzzle Maximum Velocity Chamber Pressure (psi) Round (feet/secondy" X 1000 Measured feet from muzzle. Measured by piezoelectric pressure transducer.

EXAMPLE 3 A 5.56 mm mold is assembled and filled with 23.13 grams of plasticized dynamite grade fibrous nitrocellulose prepared in Example 1. The plasticized nitrocellulose fibers are molded at a temperature of 75 C., and a pressure of 22,000 psi for about 1 minute. The resulting propellant charge is homogeneous as is evidenced by complete transparency. The cartridge is fitted with a primer, booster, and bullet as described in Example 2. The cartridge does not burn completely upon initiation of the primer and booster and ballistics are poor.

EXAMPLE 4 Plasticized fibrous nitrocellulose is prepared employing the same process as described in Example 1. The plasticizer solution is comprised of 15 parts of nitroglycerin and 15 parts of triacetin in 250 parts of isopropanol. This solution is mixed with 70 parts of fibrous nitrocellulose having a 12.2 percent nitrogen content and 200,000 seconds viscosity as measured according to ASTM D 301.

The resulting plasticized fibrous nitrocellulose fibers are free-flowing and have the following composition:

Nitrocellulose 70% Nitroglycerin 15% Triacetin 15% These fibers are molded into opaque caseless propellant chargesand are assembled into rounds of caseless ammunition following the procedures and conditions as set forth in Example 2.

Ballistic results from firing of four rounds in a 5.5 6 mm rifle are as follows:

Muzzle Maximum Velocity Chamber Pressure (psi) Round (feet/second)* X 1000 Measured 15 feet from muzzle. Measured with a piezoelectric pressure transducer.

The plasticized nitrocellulose fibers burn completely. The bullets develop muzzle velocities substantially equivalent to velocities obtained from conventional ammunition.

Various burning rate modifiers, mechanical property modifiers, stabilizers, and oxidizers can be incorporated into the fibrous nitrocellulose in addition to the plasticizer.

While the process of this invention is particularly adaptable for manufacturing propellant charges for use in caseless ammunition, other uses of these propellant charges are contemplated. Such uses of these propellant charges include propellant charges for power actuated tools, for gas generators, for pulsed power in magnetohydrodynamic applications, and as consumable cartridge cases.

As will be evident to those skilled in the art, various modifications can be made or followed, in light of the foregoing disclosure and discussion, without departing from the spirit or scope of the disclosure or from the scope of the claims.

What we claim 'and desire to protect by Letters Patent is:

l. The method or preparing a propellant charge from fibrous nitrocellulose, said method comprising:

a. dissolving a plasticizer for nitrocellulose in a volatile solvent to form a plasticizing solution, said solvent being a non-solvent for nitrocellulose,

b. admixing fibrous nitrocellulose with the plasticizing solution until the fibrous nitrocellulose fibers have absorbed the desired amount of plasticizer,

c. removing the volatile solvent from the admixture,

d. recovering plasticized fibrous nitrocellulose fibers substantially free of solvent, and

e. molding the plasticized fibrous nitrocellulose fibers to form a strong, consolidated propellant charge in which the individual fibers of the fibrous nitro-cellulose retain their identity.

2. The method of claim 1 wherein the plasticizer is comprised of nitroglycerin.

3. The method of claim 2 wherein the weight ratio of plasticizer to fibrous nitrocellulose is from about 1:9 to about 3:7.

4. The method of claim 3 wherein the plasticizer solvent is isopropanol.

5. The method of claim 3 wherein the plasticizer solvent is methylene chloride.

6. The method of preparing a caseless cartridge from dynamite grade nitrocellulose, said method comprising:

a. dissolving a plasticizer comprised of nitroglycerin in a volatile solvent to form a plasticizing solution, said solvent being a non-solvent for nitrocellulose,

b. admixing fibrous nitrocellulose with the plasticizing solution until the fibrous nitrocellulose fibers have absorbed the desired amount of plasticizer,

c. removing the volatile solvent from the admixture,

d. recovering plasticized fibrous nitrocellulose fibers substantially free of solvent, and

e. molding the plasticized fibrous nitrocellulose at a temperature of from about 35 C. to about 50 C., at a pressure of about 12,000 psi to about 16,000 psi for about I second to about seconds, and f. recovering a caseless cartridge in which the individual fibers of fibrous nitrocellulose retain their identity. 

2. The method of claim 1 wherein the plasticizer is comprised of nitroglycerin.
 3. The method of claim 2 wherein the weight ratio of plasticizer to fibrous nitrocellulose is from about 1:9 to about 3:7.
 4. The method of claim 3 wherein the plasticizer solvent is isopropanol.
 5. The method of claim 3 wherein the plasticizer solvent is methylene chloride.
 6. The method of preparing a caseless cartridge from dynamite grade nitrocellulose, said method comprising: a. dissolving a plasticizer comPrised of nitroglycerin in a volatile solvent to form a plasticizing solution, said solvent being a non-solvent for nitrocellulose, b. admixing fibrous nitrocellulose with the plasticizing solution until the fibrous nitrocellulose fibers have absorbed the desired amount of plasticizer, c. removing the volatile solvent from the admixture, d. recovering plasticized fibrous nitrocellulose fibers substantially free of solvent, and e. molding the plasticized fibrous nitrocellulose at a temperature of from about 35* C. to about 50* C., at a pressure of about 12,000 psi to about 16,000 psi for about 1 second to about 10 seconds, and f. recovering a caseless cartridge in which the individual fibers of fibrous nitrocellulose retain their identity. 